A PET (Positron Emission Tomography) system is employed as a medical imaging and diagnosis device (for example, see Japanese Laid-Open Patent Publication No, 2005-312930). The PET system is a device for making a picture of a body distribution of a positron labeling agent injected into the human body. As shown in FIG. 5, it is well known that a tunnel 2 is formed in a gantry 1 and a subject is laid on a top board 4 of an examining table 3, and the top board 4 with the subject is inserted into the tunnel 2. A number of detectors are incorporated in the gantry 1 for detecting radioactive rays.
For improvement of the PET systems, the field of view in a direction of the body axis of the subject has been discussed. Currently, each detector is arranged in a region whose length is limited in a direction of the body axis of the subject, and thereby, the field of view is as small as about 15 cm to 25 cm long. However, it is certain that the field of view in the direction of the body axis will be largely increased in the future by significantly enlarging the gantry 1 and incorporating detectors in the gantry 1 over its entire length in the future. It is anticipated, for example, that the view field in the direction of the body axis will be increased to a length of about 100 cm so as to simultaneously diagnose the entire torso of the subject. It is also foreseeable that the view field in the direction of the body axis will be increased to a length of about 180 cm so as to simultaneously diagnose the whole body from the top of the head to the toes of the subject.
In such cases, however, there will be a problem that maintenance becomes difficult because an operator cannot easily access detectors located at the middle of the gantry in the direction of the body axis, for example, in order to change the detectors.
Accordingly, an object of the present invention is to eliminate the problem of the detector's maintenance in a PET system, when the field of view in the direction of the body axis of the PET system is significantly enlarged.